This application claims the priority of German patent application 10 2008 031 910.4, filed Jul. 8, 2008, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an arrangement for the (especially temporary) force-free holding of a bearing system having an axis of rotation.
Highly sensitive optical or electrical scanning systems, such as telescopes, require play-free bearing systems which should influence a driving mechanism of the scanning system as little as possible. This means that the bearing system must generate torque reactions that are as low as possible. An (absolutely) backlash-free bearing system, particularly over large temperature differences, is achieved, for example, by highly preloaded bearing systems which require high driving torques.
So-called Flexpivot bearings have been successful for swiveling movements in an angular range of approximately +/−25°. Such bearings, which maintain their axis of rotation very precisely by way of an elastic deformation of integrated flat spring elements, have the advantage that no friction occurs between rotating parts of the bearing system. However, when the kinematic design is optimal, at zero gravity, Flexpivot bearings are very sensitive to lateral and axial forces, such as generally occur during a rocket launch by which the scanning system is entered into an orbit.
So-called “Hold-Down and Release” mechanisms (HDRM) are used in order to relieve the bearings of the scanning systems. These mechanisms are closed during the rocket launch, and opened in orbit, so that the scanning system can operate in accordance with its determination. A frequent problem occurring with HDRMs is that there is a small overdetermination, so that a deformation of the Flexpivot bearing cannot be completely prevented, and the operability of the Flexpivot bearing may be impaired.
One object of the present invention, therefore is to provide a simple arrangement for (especially temporary) force-free holding of a bearing system having an axis of rotation, without an overdetermination of the holding.
Another object of the invention is to provide such an arrangement which easily permits unlocking for release of the bearing system.
These and other objects and advantages are achieved by the holding arrangement according to the invention, which comprises a cylindrical hollow axle for concentrically receiving and holding a bearing system having an axis of rotation. The center axis or axis of symmetry of the cylindrical hollow axle coincides with the axis of rotation of the bearing system when the latter is received and held by the cylindrical hollow axle. The arrangement also comprises a bearing shell which can be fastened to the hollow axle by a hold-down and release mechanism, in such a manner that all lateral and axial forces applied to the arrangement can be transmitted via the cylindrical hollow axle into axle receiving devices, while the bearing system is not acted upon by a load.
The disposition of the bearing system in the cylindrical hollow axle, which is connected with a bearing shell controlled by the hold-down and release mechanism, achieves an arrangement which has no overdetermination with respect to the bearing system, and can be implemented at a minimal component weight, with compact dimensions. In particular, the arrangement according to the invention permits the use of a bearing system with dimensions that are as small as possible, because the latter needs be designed only for orbital loads, and therefore can build up only low torques. In contrast, stability during the mounting of the bearing system (and particularly during a rocket launch) is provided by the arrangement, and especially by the cylindrical hollow axle. Another advantage of the invention is that it can be applied or used several times.
In one embodiment of the invention, the bearing axle surrounds the hollow axle in the circumferential direction, so that a uniform absorption of the lateral and axial forces is ensured by way of the cylindrical hollow axle.
The hollow axle is advantageously formed of two mutually symmetrically arranged, partial axles which are connected with one another by the bearing system. The lateral and axial forces applied to the arrangement are transmitted by the two partial axles into axle receiving devices, so that the bearing system is uncoupled from such forces as long as the hold-down and release mechanism is locked.
In another embodiment of the invention, the partial axles each have a flange with a bore at their mutually facing ends, for fastening and holding the bearing system, which is connected with the flanges of the partial axles. Advantageously, the bearing system is connected with the hollow axle or with the two partial axles in a material-locking manner. Such material locking can be carried out subsequently by means of an electro plasma welding system, along the entire circumference of the bearing system.
According to a further expedient embodiment of the invention, the partial axles each have a groove at their mutually facing ends on their exterior side, into which groove the bearing shell engages in a form-locking manner. In this case, the groove extends particularly along an outer circumference of the partial axle. The respective grooves advantageously have a continuous (i.e., surrounding) construction.
The bearing shell may comprise first and second bearing shell parts, which are rotatably connected with one another at their first end and which, at their second (opposite) ends, are connected with one another under high prestress by means of the hold-down and release mechanism. As a result of the two-part embodiment of the bearing shell, on the one hand a simple and firm connection with the hollow axle can take place. On the other hand, by opening the two bearing shell parts, an application of force on the hollow axle can be prevented, so that the bearing system can be used for its purpose. The connection of the two bearing shell parts at their first end and their fixing while applying a high prestress by means of the hold-down and release system permits a simply designed construction, and the reliable provision of a not overdetermined holding mechanism for the bearing system. The high prestress at the two ends permits an automatic “opening” of the bearing shell as soon as the hold-down and release mechanism no longer applies a force for pressing together the two ends.
Advantageously, a spring element may also be provided between the two ends of the bearing shell parts. The spring element causes a defined opening of the bearing shell parts when the hold-down and release mechanism for unlocking the arrangement according to the invention is triggered.
According to a further embodiment of the invention, the hold-down and release mechanism may comprise a bolt separating mechanism, for example, in the form of a known Frangibolt mechanism which, when correspondingly controlled, disconnects the mechanical connection of the two ends of the bearing shell parts and thereby terminates its force effect on the hollow axle.
For absorbing forces occurring during a rocket launch, the hollow axle may be formed particularly of a highly rigid material, such as titanium. As explained above, it thereby becomes possible to dimension the bearing system only for orbital loads, so that it builds up only low torques, as required for highly precise scanning elements. Correspondingly, the bearing shell is made of the same high-strength material (titanium).
It is further provided that the hollow axle may be manufactured in one setting.
In the arrangement according to the invention, the bearing system advantageously comprises a tension-free Flexpivot bearing, which very precisely maintains its axis of rotation by way of an elastic deformation of integrated flat spring elements, without causing any friction between the rotating parts. Flexpivot bearings of this type are known from the state of the art.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.